This application claims priority of Japanese Patent Application No. 2001-186779, filed on Jun. 20, 2001.
1. Field of the Invention
The present invention relates to a range finder used for supporting a driver when the driver drives an automobile. More particularly, the present invention relates to a range finder for finding a range to a target, which is running in front, by image realization, when a plurality of cameras or image pickup elements are used.
2. Description of the Related Art
In order to enhance the convenience and safety of driving an automobile, a driver support system has been recently put into practical use. In this driver support system, range finding to find a range to a vehicle running in front is one of the factors to be provided. A range to a vehicle running in front has been detected until now by a range finding system, in which the range is found by image realization with compound-eye cameras.
In the above conventional range finding system in which compound-eye cameras are used, a range to a vehicle running in front is found as follows. A vehicle running in front is photographed by two cameras, which are mounted at a predetermined interval on a vehicle running behind, or by image pickup elements such as image sensors. The parallax of the same object (the vehicle running in front) on the thus obtained two images is utilized, and a range to the vehicle running in front is found from this parallax by the principle of triangulation.
On the other hand, in some cases, distortion is caused on an image obtained by each camera when the optical system is distorted. When the obtained image is distorted, it impossible to accurately calculate the parallax, and range finding is erroneously conducted. In order to solve the above problems, a distorted image photographed by each camera is corrected by a distortion correcting circuit so that the distorted image can be processed to an image having no distortion, and then a range to a target is found.
However, in the above conventional range finding method, as the entire image photographed by each camera must be corrected, it becomes necessary to provide a large-scale distortion correcting circuit and a memory to be incorporated into the distortion correcting circuit. Further, since the entire image must be corrected, a quantity of processing necessary for correction is increased, which causes a drop in the processing speed. Furthermore, even if the distortion is corrected, a fluctuation is caused in the pixel values of the images photographed by the right and left cameras. Therefore, it is difficult to accurately calculate the parallax. Furthermore, the above conventional range finding is disadvantageous in that a road surface (shadows, white lines and characters on the road) becomes an object of range finding in some cases.
The present invention has been accomplished to solve the above problems of the conventional range finding method for finding a range to a target by image realization. It is an object of the present invention to provide a range finder capable of finding a range to a target at high speed without having an error in range-finding caused by distortion of an image without providing a large-scale correcting circuit and memory.
It is another object of the present invention to provide a range finder capable of accurately finding a range to a target by correcting a fluctuation caused between images photographed by a right and a left camera.
It is still another object of the present invention to provide a range finder capable of accurately finding a range to a target without having an error in range-finding caused by a road surface.
In order to solve the above problem, the present invention provides a range finder for finding a range to a target by image realization comprising: a first and a second imaging device arranged at a predetermined interval; a pattern extracting section for extracting a first pattern having a predetermined size and the first positional information from a first image of the target which has been made by the first imaging device; a correlation processing section for detecting a second pattern having the second positional information, which is most correlated with the first pattern, from a plurality of horizontal or vertical lines located at positions corresponding to the first positional information in the second image of the target which has been made by the second imaging device; and a parallax calculating section for finding parallax from the first and the second positional information. When a correlation is found by a plurality of upward and downward lines, it is possible to accurately find parallax without conducting correction with respect to the distortion and axial misalignment.
In a range finder of the present invention, the correlation processing section finds a correlation with the first pattern for every a plurality of horizontal or vertical lines, and the second pattern having the second positional information, which is most correlated with the first pattern, is detected according to the plurality of pieces of correlation which have been found. A correlation is found by a plurality of upward and downward lines, and when it is judged how far a correlating position on each line departs from a vertical line, a pattern can be accurately realized even if other confusing patterns exist.
In a range finder of the present invention, it is preferable that the first image is divided into a proximity region, which can be easily correlated, and a background region which is difficult to be correlated, and the correlation processing section finds a correlation with the first pattern for every a plurality of horizontal or vertical lines only when the first pattern exists in the background region. In this constitution, only when the pattern is realized in a background region in which it is difficult to correlate, a correlation is found by a plurality of upward and downward lines.
It is preferable that a range finder of the present invention further comprises an image correcting section for detecting a state of misalignment of the first or the second image according to the correlation of the first pattern with the second pattern for every a plurality of horizontal or vertical lines which has been found by the correlation processing section, and for correcting the first or the second image according to the state of the detected misalignment.
Further, it is preferable that a range finder of the present invention further comprises an alarm generating section for generating an alarm when a value of correlation, which is obtained in the case where the correlation processing section detects the second pattern, is compared with a correlation reference value and when the value of correlation is not more than a correlation reference value. When the distortion of an image plane and the misalignment of an axis are large and it is impossible to accurately conduct range finding, an alarm is generated.
In order to solve the above problems, a range finder for finding a range to a target by image realization of the present invention comprises: a first and a second imaging device arranged at a predetermined interval; a density difference detecting section for finding a density difference between the first image and the second image from the first image of the target, which has been made by the first imaging device, and the second image of the target which has been made by the second imaging device; an image density correcting section for correcting density of the first or the second image according to the density difference between the first and the second image; a pattern extracting section for extracting a first pattern having a predetermined size and first positional information from the first image; a correlation processing section for detecting a second pattern having the second positional information, which is most correlated with the first pattern, in the second image of the target which has been made by the second imaging device; and a parallax calculating section for finding parallax from the first and the second positional information. When a difference of density between the right and the left image is found and one of the images is corrected by utilizing the difference in density, it becomes possible to accurately conduct range finding.
In order to solve the above problems, a range finder for finding a range to a target by image realization of the present invention comprises: a first and a second imaging device arranged at a predetermined interval; a density difference detecting section for finding a density difference between the first image and the second image from the first image of the target, which has been made by the first imaging device, and the second image of the target which has been made by the second imaging device; a pattern extracting section for extracting a first pattern having a predetermined size and first positional information from a first image; an image density correcting section for correcting density of the first pattern according to the density difference between the first and the second image; a correlation processing section for detecting a second pattern having the second positional information which is most correlated with the corrected first pattern in the second image; and a parallax calculating section for finding parallax from the first and the second positional information. When a difference of density between the right and the left image is found and only the pattern is corrected by utilizing the difference of density, it becomes possible to accurately conduct range finding.
It is preferable that a range finder of the present invention further comprises a parameter setting section for setting a parameter necessary for processing conducted by the correlation processing section according to a density difference between the first and the second image. When the parameter necessary for correlation processing is changed by the difference of density found from the right and the left image, range finding can be more accurately conducted.
In order to solve the above problems, a range finder for finding a range to a target by image realization of the present invention comprises: a first and a second imaging device arranged at a predetermined interval; a pattern extracting section for extracting a first pattern having the first positional information containing a range finding target from the first image of the target which has been made by the first imaging device; a correlation processing section for detecting a second pattern having the second positional information, which is most correlated with the first pattern in the second image of the target which has been made by the second imaging device; a parallax calculating section for finding parallax from the first and the second positional information; a range finding section for finding a range to the range finding target by the parallax; a realizing section for realizing a height of the range finding target according to the position in the first or the second image of the range finding target and according to the result of range finding conducted by the range finding section; and a nullifying section for nullifying the result of range finding conducted by the range finding section in the case where the height of the range finding target is smaller than the reference height. The height of the range finding target is realized by the position in the image, the range of which was found, and by the result of range finding. When the height is not more than a predetermined height from the ground, the target of range finding is realized as characters and shadows on a road, and the result of range finding is nullified.
It is preferable that a range finder of the present invention further comprises a road surface position correcting section for detecting a white line in the first or the second image and for finding a range to a forward end portion of the white line and for correcting a road face position, which becomes a reference to realize the height of the range finding target, from the value of range finding of the forward end portion of the white line. When the position of the ground in the image is corrected by the result of realization of a white line on a road, it becomes possible to judge a height agreeing with the road environment.
A range finder of the present invention further comprises a road surface correcting section for detecting a third pattern having the same characteristic as that of the white line from the first or the second image and for finding a range to the forward end portion of the third pattern and for correcting a road face position, which becomes a reference to realize the height of the range finding target, from the value of range finding of the forward end portion of the third pattern. Another pattern such as a character on a road surface having the same characteristic as that of a white line on the road surface is extracted from an image, and its forward end portion is used as a reference and the position of the ground in the image is corrected. Due to the foregoing, it becomes possible to judge a height agreeing with the road environment.
In a range finder of the present invention, it is preferable that the reference value correcting section corrects a reference value according to a plurality of range finding values of the forward end portion of the third pattern. The reference value is corrected according to data sent from a plurality of positions.
Further, in a range finder of the present invention, it is preferable that the reference value correcting section corrects the road surface position by utilizing only a range finding value in a predetermined range of values in the plurality of range finding values of the forward end portion of the third pattern. Without using data outside the predetermined range of values, the reference value is more accurately corrected.
In order to solve the above problems, a range finder for finding a range to a target by image realization of the present invention comprises: a first and a second imaging device arranged at a predetermined interval; a pattern extracting section for extracting a first pattern having a predetermined size and the first positional information containing the range finding target from the first image of the target which has been made by the first imaging device; a correlation processing section for detecting a second pattern having the second positional information, which is most correlated with the first pattern in the second image of the target which has been made by the second imaging device; a parallax calculating section for finding parallax from the first and the second positional information; a range finding section for finding a range to the range finding target by the parallax; a judging section for judging whether or not the range finding target exists in a range finding objective region according to the result of range finding to find a range to the target and also according to the position of the range finding target in the first or the second image; and a nullifying section for nullifying the result of range finding conducted by the range finding section in the case where the range finding target exists outside the range finding objective region. When range finding is conducted only in a predetermined range, the processing time of range finding can be reduced.
A range finder further comprises a height realizing section for realizing a height of the range finding target according to the position of the range finding target in the first or the second image, wherein the nullifying section does not nullify the result of range finding conducted by the range finding section in the case where the height is larger than a predetermined reference value of the height even if the range finding target exists outside the objective region of range finding. In the case where the height is a predetermined value although it is outside the range finding objective region, it becomes possible to more accurately realize a range finding target when it is made to be a range finding object.